A suspension arrangement of the above-referenced type is generally known, for example, from EP 0 425 885 B1 (from FIG. 5 onward). This suspension arrangement is a hydropneumatic suspension system, the cylinder chamber and the annular chamber of the spring cylinder being connected in each case to a hydropneumatic spring accumulator, so that a pneumatic pressure acts indirectly in each case, via a hydraulic medium, on both sides of the piston of the spring cylinder. This gives rise to two forces which act on the piston in opposite directions and the difference between which gives a load-bearing force for supporting the load.
The known suspension system has proven very successful in practice. However, pneumatic suspension generally have the disadvantage that changes in ambient temperature influence the pressure of a pneumatic spring medium to an extremely pronounced extent, so that the load-bearing and spring properties likewise change in a temperature-dependent manner. This also applies to the vehicle level in the static state. In the case of the suspension system according to EP 0 425 885 B1, this temperature influence is indeed reduced somewhat, because two pressures act on the piston of the spring cylinder in opposite directions. However, there is still a need for improvement.
The object of the present invention is thus to improve a suspension arrangement of the type mentioned such that, in practice, the use properties are not dependent on temperature fluctuations. This applies, in particular, to a static level position of the spring cylinder, in order that the respective vehicle level remains more or less constant at different temperatures.
It is provided according to the invention that an additional spring cylinder is arranged in the region of the piston rod of the spring cylinder such that the piston rod can be telescopically changed in length. The additional spring cylinder comprises an additional cylinder and an additional piston which is guided therein and has an additional piston rod guided in the outward direction, the additional spring cylinder with these constituent parts forming part of the piston rod. It is preferred here for the additional cylinder to be connected in a fixed (rigid) manner to the piston-side part of the piston rod, while the outwardly guided additional piston rod in practice forms, by way of its free end, the end of the variable-length piston rod and, for this purpose, has an end connecting element for vehicle-mounted connection. However, the additional spring cylinder may also be arranged the other way round, i.e. it is possible for the additional piston rod to be connected to the piston rod and for the additional cylinder to be connected to the connecting element of the vehicle.
According to the invention here, the additional spring cylinder is subjected at least to a counterpressure of an elastically compressible, in particular pneumatic opposing spring medium, in the region of an additional annular chamber and/or of an additional working chamber. This design makes it possible, in dependence on the load occurring in the respective application case, for the working pressure, the counter pressure and those surfaces of the piston and of the additional piston which are subjected to these pressures to be configured such that in a static state subjected to the action of the load, on the one hand, the piston is located in an extension end stop relative to the cylinder, and, on the other hand, the additional piston is located in a compression end stop relative to the additional cylinder. In this static position, in the case of an increase in temperature, the thus likewise increasing pressures advantageously does not result in a change in the static level. In the case of a dynamic compression movement from the static position, only the piston is moved into the cylinder, counter to the working pressure, while the additional piston remains in its compression end stop in the additional cylinder. In the case of a dynamic extension movement out of the static position, the piston is located in its extension end stop, and only the additional piston moves, by way of the additional piston rod, in the extension direction in the additional cylinder.